1. Field of the Invention
The present invention relates to a rotary driving system for driving a robot arm by a planetary roller speed reducer with a plurality of planetary rollers disposed around a sun roller.
2. Related Background Art
Conventional planetary roller speed reducer with planetary rollers constructed in two stages includes those which have been disclosed in Japanese patent application Laid-open No. 58-39873, Japanese patent application Laid-open No. 58-57554 and Japanese patent application Laid-open No. 60-18651.
Those speed reducers disclosed as above were not equipped with turning angle detection means for detecting turning angles of an output shaft integrally therewith, but a position detector such as a rotary encoder or the like was provided particularly on the output shaft of a motor for detection of the turning angles.
Since the turning angles are detected by the position detector such as an encoder which is mounted on the motor output shaft, when said conventional speed reducers are used on an apparatus requiring high precision for placing a robot arm and others in position, error is inevitable such that a positioning reproducibility of high precision is not realizable due to slip arising internally.